Uptime is also a sales and marketing point, regardless of real-world usage. Business folks in service-providing companies will usually expect high availability by default, only tempered by the cost and reality of more nines.

Also, in addition to perception/reputation issues, B2B contracts typically include an SLA, and nobody wants to be in breach of contract.

I think the parent you're replying to is wrong, because I've worked at small companies selling into large enterprise, and the expectation is basically 24/7 service availability, regardless of industry.